1. Field of the Invention
The present invention relates to compositions useful in ophthalmology. In particular, this invention relates to ophthalmic compositions comprising biocompatible, polymerizable, bioadhesive, surface-active, fluorinated monomers. These monomers, spontaneously ordered in vivo to produce liquid-crystalline phases, can be polymerized in situ to repair torn, ruptured or detached retinal tissue.
2. Description of Related Art
Retinal detachments and tears are conventionally repaired using media which exert pressure on the retinal tissues to reposition them such that they are confluent with the underlying tissue, the retinal pigment epithelium (RPE), responsible for nourishing and supporting metabolism of the retinal tissue. Typical repositioning media function as a tamponade, and are ideally neither viscous nor adherent to biological tissue. The density of the repositioning media can be either significantly higher or lower than that of the vitreous body. The principle involves exploiting gravity to maintain approximation of displaced retina at proximal RPE: if the displacement requires upward approximation, then a medium of density less than vitreous is chosen, and if downward, then a medium of density greater than vitreous is chosen. For example, a retinal tear in the macular area may be repositioned using a highly dense media with the patient lying on his back, or with a low density media with the patient lying on his face. If the retinal break is toward the top of the head, repositioning is carried out with gases, and if the break is toward the bottom of the head, repositioning is carried out with media having a high specific gravity.
Examples of repositioning media in use today include silicone oil, fluorocarbon and perfluorocarbon liquids (such as SF.sub.6, C.sub.3 F.sub.8, and C.sub.2 F.sub.6), nitrogen gas and air. See, for example, Ferrone et al., "The efficacy of silicone oil for complicated retinal detachments in the pediatric population," Arch. Ophthalmol., 112/6, p. 773-777 (1994).
One disadvantage of these conventional techniques is that the resulting reattachment produced by reapproximation using repositioning media often is transient. The desired reattachment often fails upon removal or absorption of the repositioning media. Additionally, the use of dense repositioning media can be awkward, requiring certain positioning of the head to maintain a favorable pressure for attachment. The media may result in complications including scarring, glaucoma, or corneal opacification, or may prove toxic upon extended exposure.
To help prolong the duration of the intended reattachment, once the torn or detached retina is positioned correctly, a procedure called retinopexy can be used to produce adhesion between retina and RPE. Retinopexy can be achieved by using laser, diathermy or cryogenic techniques which induce wounds that stimulate reaattachment following the growth of connective tissue. The connective tissue results in rigid attachment of retinal tissue to the RPE. Retinopexy can also be achieved using either biological or nonbiological adhesives such as fibrin or thrombin, or nitrocellulose and cyanoacrylates, respectively. The use of these adhesive materials also results in rigid attachment between retina and RPE. Yet another means of achieveing retinopexy involves the use of a "retinal tack." Retinal tacks are typically stainless steel tacks which bind the retina to the RPE. See, for example, De Juan et al., "Mechanical retinal fixation using tacks," Ophthalmology, 94/4, p. 337-340 (1987). Retinopexy, however achieved, can be both painful and temporary. Since the resulting attachments tend to be rigid, possessing considerably larger elastic moduli than the retina itself, normal ocular motions which conventionally are accommodated by the elastic retina can result in new tears and detachments in the vicinity of previous repairs.
What is needed is an alternate means for repairing torn or detached retinal tissue which eliminates inadequacies of the approaches described above.